1. Technical Field
Methods for forming a capacitor having a storage electrode are disclosed wherein the capacitor is formed of ruthenium (hereinafter, referred to as xe2x80x98Ruxe2x80x99) film, and more particularly, methods for forming a capacitor having a storage electrode formed of Ru film whereon dielectric films having the excellent deposition characteristics are formed using high dielectric constant materials such as Ta2O5 film, BST film, PZT film, SBT film or BLT film.
1. Description of the Related Art
As the cell size is decreased due to high integration of semiconductor devices, it is difficult to obtain sufficient capacitance proportional to the surface area of storage electrode.
Specifically, in case of high integration of DRAM device having a unit cell consisting of a MOS transistor and a capacitor, the significant factor for high integration is to increase the capacitance of a capacitor which occupies much space of unit cell.
Accordingly, a convenient method of increasing the capacitance of a capacitor following the equation of (Eoxc3x97Erxc3x97A)/T (Eo: permitivity of vacuum, Er: dielectric constant of dielectric film, A: surface area of capacitor, T: thickness of dielectric film) is to minimize the thickness T of dielectric film by thinning the dielectric film or to increase the surface area A of capacitor by forming the capacitor having three dimensional structures such as concave type or cylinder type.
However, high integration of semiconductor devices results in limit of the process for forming a capacitor. In order to overcome the limit, a dielectric film having high dielectric constant is selected from the group consisting of Ta2O5 film, BST film, PZT film, SBT film or BLT film instead of the conventional dielectric film formed of silicon.
Additionally, as the dielectric films having high dielectric constant are used, storage electrodes are formed of iridium film, platinum film or conductive oxide film as well as Ru film.
Although not shown in the drawings, a conventional method for forming a capacitor of a semiconductor device is described.
First, a planarized lower insulating layer is first formed on a semiconductor substrate comprising a device isolation film, a word line and a bit line.
The lower insulating layer is formed of insulating materials having high fluidity such as BPSG (Boro Phospho Silicate Glass).
A storage electrode contact hole is formed to expose a predetermined portion of the semiconductor substrate.
The storage electrode contact hole is formed by etching the lower insulating layer via a photo-etching process using a storage electrode contact mask.
Then, a contact plug is formed to fill the storage electrode contact hole.
The contact plug comprises a stacked structure of polysilicon film/Ti film/TiN film.
After a sacrificial insulating film is formed on the entire surface of the resultant structure, a trench-type storage electrode region is formed by etching the sacrificial insulating layer via a photo-etching process using a storage electrode contact mask.
A Ru film, metal layer for lower electrode connected to the contact plug is formed on the entire surface of the resultant structure. Here, the Ru film is deposited via a chemical vapor deposition (hereinafter, referred to as xe2x80x98CVDxe2x80x99) method.
A storage electrode is formed of the Ru film remaining on the surface of the storage electrode region via the planarization etching process.
A dielectric film, Ta2O5 film, is formed on the entire surface of the resultant structure including the storage electrode formed of Ru film via a MOCVD (metal organic chemical vapor deposition) method. Here, the Ta2O5 film reacts with Ru film and then rapidly grows on the top side of the storage electrode region, thereby resulting in overhang phenomenon (see FIG. 1).
Recently, in order to overcome the overhang phenomenon generated from the process of depositing dielectric films, the following process steps are used:
1. reducing the whole deposition speed by lowering the chamber temperature;
2. reducing the reaction speed of source and electrode surface by reducing the amount of source;
3. reducing the reaction speed of source and reactant gas by reducing the amount of reactant gas; and
4. reducing the partial pressure of source by increasing the amount of carrier gas.
However, the low deposition speed due to the step 1 results in degradation of film quality and throughput characteristics. Although the steps 2, 3 and 4 may improve step coverage, the decrease of deposition speed in the steps also results in throughput characteristics.
As described above, the conventional method for forming a capacitor of a semiconductor device generates the overhang phenomenon when dielectric films of high dielectric constant are formed on storage electrode formed of Ru film having the three dimensional structure. As a result, it is impossible to perform the subsequent process, and yield and productivity of device are degraded.
Accordingly, a method for forming a capacitor is disclosed wherein the capacitor comprises a dielectric film formed via two-step deposition process to have excellent deposition characteristics, thereby improving yield and productivity of semiconductor device and embodying high integration of semiconductor device.
One disclosed method for forming a capacitor having a Ru storage electrode on a semiconductor device comprising:
(a) forming a storage electrode consisting of Ru on a semiconductor substrate;
(b) forming dielectric films on the storage electrode, the dielectric films comprising a stacked structure of a first dielectric film and a second dielectric film formed at a different deposition rate from the first dielectric film; and
(c) forming an upper electrode on the dielectric film.
A ratio of deposition rate of the first dielectric film:the second dielectric film falls within the range of 1:1.5xcx9c10.
The deposition rate of the first dielectric film is ranging from 1 to 10 xc3x85/min and the deposition rate of the second dielectric film is ranging from 5 to 50xc3x85/min.
A partial pressure of source gas in the formation process of the first dielectric film is lower than that of source gas in the formation process of the second dielectric film.
The ratio of a partial pressure of source gas in the formation process of the first dielectric film:the second dielectric film falls within the range of 1:1.5xcx9c100.
The formation process of the first dielectric film is performed by a MOCVD method under the conditions of:
1) at a chamber temperature ranging from 250 to 750xc2x0 C.;
2) using a source selected from the group consisting of Ta(OC2H5)5, Ba(METHD)2, Sr(METHD)2, Ti(MPD)(THD)2 and mixtures thereof which is subject to inflow into a reaction chamber at a flow rate ranging from 0.001 to 0.1 g/min;
3) using an inert gas as a carrier gas which is subject to inflow into the reaction chamber at a flow rate ranging from 10 to 1000 sccm as a carrier gas; and
4) using a reactant gas selected from the group consisting of O2, N2, N2O, NH3 and mixtures thereof which is subject to inflow into the reaction chamber at a flow rate ranging from 1 to 1000 sccm.
The inert gas is selected from the group consisting of N2, Ar, Xe and mixtures thereof.
The method further comprises a step of performing a thermal treatment process onto the dielectric film after the step (b), using at least one process selected from the group consisting of plasma treatment, UVxe2x80x94O3 treatment, RTP annealing, furnace annealing and combinations thereof.
The step (b) is repeatedly performed more than 2 times.
There is also provided a method for forming a capacitor having a Ru storage electrode on a semiconductor device comprising:
(a) forming and selectively patterning a sacrificial layer on a semiconductor substrate to form a trench;
(b) forming a diffusion barrier layer and a storage electrode on the resultant sutructure;
(c) forming dielectric films on the storage electrode, the dielectric films comprising a stacked structure of a first dielectric film and a second dielectric film formed at a different deposition rate from the first dielectric film; and
(d) forming an upper electrode on the surface of the dielectric film.
A ratio of deposition rate of the first dielectric film:the second dielectric film falls within the range of 1:1.5xcx9c10.
The deposition rate of the first dielectric film is ranging from 1 to 10 xc3x85/min and the deposition rate of the second dielectric film is ranging from 5 to 50 xc3x85/min.
A partial pressure of source gas in the formation process of the first dielectric film is lower than that of source gas in the formation process of the second dielectric film.
The ratio of a partial pressure of source gas in the formation process of the first dielectric film:the second dielectric film falls within the range of 1:1.5xcx9c100.
The formation process of the first dielectric film is performed by a MOCVD method under the conditions of:
1) at a chamber temperature ranging from 250 to 750xc2x0 C.;
2) using a source selected from the group consisting of Ta(OC2H5)5, Ba(METHD)2, Sr(METHD)2, Ti(MPD)(THD)2 and mixtures thereof which is subject to inflow into a reaction chamber at a flow rate ranging from 0.001 to 0.1 g/min;
3) using an inert gas as a carrier gas which is subject to inflow into the reaction chamber at a flow rate ranging from 20 to 6000 sccm; and
4) using a reactant gas selected from the group consisting of O2, N2, N2O, NH3 and mixtures thereof which is subject to inflow into the reaction chamber at a flow rate ranging from 1 to 1000 sccm.
The formation process of the second dielectric film is performed by a MOCVD method under the conditions of:
1) at a chamber temperature ranging from 250 to 750xc2x0 C.;
2) using a source selected from the group consisting of Ta(OC2H5)5, Ba(METHD)2, Sr(METHD)2, Ti(MPD)(THD)2 and mixtures thereof which is subject to inflow into a reaction chamber at a flow rate ranging from 0.001 to 0.1 g/min;
3) using an inert gas as a carrier gas which is subject to inflow into the reaction chamber at a flow rate ranging from 10 to 1000 sccm as a carrier gas; and
4) using a reactant gas selected from the group consisting of O2, N2, N2O, NH3 and mixtures thereof which is subject to inflow into the reaction chamber at a flow rate ranging from 1 to 1000 sccm.
The inert gas is selected from the group consisting of N2, Ar, Xe and mixtures thereof.
The method further comprises a step of performing a thermal treatment process onto the dielectric film after the step (c), using at least one process selected from the group consisting of plasma treatment, UVxe2x80x94O3 treatment, RTP annealing, furnace annealing and combinations thereof.
The step (c) is repeatedly performed more than 2 times.
An important principle of the disclosed methods is to deposit a first dielectric film having a predetermined thickness on a storage electrode at low deposition speed by regulating the amount of added gas and source under a predetermined chamber temperature and then deposit a second dielectric film having a predetermined thickness on the first dielectric film at high deposition speed, thereby obtaining dielectric films having a stacked structure.
Here, the process of depositing the first dielectric film is performed at low deposition speed ranging from 1 to 10 xc3x85/min by adding a large amount of inert gas or decreasing the amount of source.
Also, the process of depositing the second dielectric film is performed at higher deposition speed ranging from 5 to 50 xc3x85/min and having the same amount of source of the first step by inhibiting inflow of a large amount of carrier gas or inert gas added therein.